I don't think it's internal friction so much as it is the rings not sealing perfectly.
Anytime you have a leak in a cylinder, it introduces hysteresis into the pressure/volume curve of the compression/expansion cycle. More fuel has to be burned to offset these hysteresis losses and the engine gets bad gas mileage and gets hot.
Engines get better gas mileage after break in more because the rings start sealing better more than mechanical friction is reduced.
Anytime you have a leak in a cylinder, it introduces hysteresis into the pressure/volume curve of the compression/expansion cycle. More fuel has to be burned to offset these hysteresis losses and the engine gets bad gas mileage and gets hot.
Engines get better gas mileage after break in more because the rings start sealing better more than mechanical friction is reduced.